The University of North Carolina Highway Safety Research Center has conducted research[1] leading to publication by the Federal
Highway Administration (USA) of an implementation manual for a so-called "Bicycle
Compatibility Index" ("BCI").[2]
This critique addresses mainly the implementation manual.

Really only a comfort index, and less than satisfactory as one

Level of service as conventionally defined describes traffic flow: unimpeded,
congested, gridlocked. In a modern GIS database containing traffic data, an area-wide
evaluation can be carried out automatically once the parameters of a formula are included
in the database software. However, the BCI does not meet the requirement for such
analysis, for several reasons.

Though the BCI is described as a level-of-service concept, it was developed using
regression analysis of ratings of bicyclists' comfort level on roads shared with motor
traffic, paying no attention to bicyclists' mobility (and by implication, safe travel
speed), as do conventional level of service concepts.

More people want to travel at some times than at others. Weather and other factors also
affect traffic flow. The usual application of the level of service concept is to quantify
whether a road is congested, or might become congested, at one location and time
or another. Specifying level of service only in terms of location is insufficient.

The BCI formula uses measures of motorist speed and volume, and of travel lane and bike
lane/shoulder width. Mobility of bicyclists depends to a great degree on traffic signal
timing, directness of routing, terrain and congestion. Of these, only congestion is
addressed in the BCI, indirectly in terms of motor traffic volume. There is no input
reflecting bicycle or pedestrian traffic volume.

The BCI formula is based on faulty assumptions about bicyclists' use of the roadway. For
example, the formula does not consider that bicyclists may overtake in a lane to the left
of stopped or slow traffic (for example, vehicles waiting to turn right, double-parked
vehicles, or a bus picking up or discharging passengers). It only considers overtaking in
the rightmost travel lane, parking lane or bike lane. This implies overtaking the slower
or stopped traffic on its right, a move which is often hazardous, and in many cases
illegal.

In developing the BCI, bicyclists were asked to rate their comfort with overtaking motor
vehicles displayed on a video screen. Wayne Pein has published a critique of this research
method[3]. Viewing videos rather than real
traffic does indeed, as the research report indicates, allow for more uniformity of data
presented to experimental subjects, and for more convenient and faster testing. But there
was no actual bicycle riding -- and worse yet, the camera was at the curb. There was no
object in the road at the location where a bicyclist would be riding. For this reason, the
locations of the motor vehicles were not the same as they would have been with a bicyclist
present.

Bicyclists' speed affects their safety, mobility, and comfort -- their level of service.
The video clips used in the BCI development were made with a stationary camera, skewing
the perception of motorists' speed relative to that of the prospective bicyclist subjects,
and providing no input on the effects of bicyclists' speed on their need to process
information and maneuver accordingly.

There are mathematical, programming and descriptive errors in the BCI formula as
embodied in a Microsoft Excel workbook included with the report.

There is a variable for parking occupancy, but only a true/false choice as to whether
there is a parking lane, and none to indicate whether there is parallel or angle parking.
Available travel width, therefore, is undefined where there is a parking lane.

The BCI rates a street with a bike lane or shoulder higher than one with a wide outside
lane, though no difference in the safety and performance of these configurations has been
demonstrated, and bike lanes adjacent to parking may encourage bicyclists to ride within
range of opening doors of parked cars.[4]

Most car-bike collisions involve turning and crossing movements, and most impediments to
bicyclists' travel by motor vehicles also involve turning and crossing movements. The
Index accounts for only one such movement, the motorist right turn.

Effect of linear model on the contribution of motorist speed

Increased speed of motorists' overtaking bicyclists may adversely affect the
bicyclists' comfort and safety, but has little effect on bicyclists' mobility except as it
affects their making left turns. On the other hand, when motorists are stopped or
traveling slower than bicyclists, bicyclists' mobility, a real-world measure of level of
service, can be seriously reduced.

The BCI makes a deduction in its rating linearly in proportion to motorist speed. The
BCI therefore fails to measure the difference between bicyclist speed and
motorist speed, as already mentioned, but it also rates streets higher as the motor
traffic becomes more congested and increasingly impedes bicycle travel.

The implementation paper indicates that the BCI is supposed to be used only with
outside lane motor vehicle traffic flow between 90 and 900 vehicles per hour; outside lane
width between 3.0 and 5.6 meters; bike lane/shoulder width between 0.9 and 2.4 meters; and
motorist speeds between 40 and 89 km/h (25 and 55 mph). The speed and flow ranges exclude
many conditions typical of congested urban traffic.

If the person applying the BCI does not keep the data range limits in mind, it is very
likely that out-of-range data will be input. If the formula is applied automatically to
GIS data, results based on out-of-range data are almost certain to go undetected.

The following examples (for which data are given in a table, below), illustrate the
inaccurate results the BCI gives under some typical urban traffic conditions that produce
out-of-range data.

In a right lane too narrow for motorists and bicyclists to share side by side, and with
no other lane available for bicycle travel, the most favorable possible motorist speed,
according to the BCI, is zero -- gridlock.

In a wide outside lane, or an outside lane with a shoulder or bike lane to its right,
the BCI also favors stopped motor traffic over moving traffic, even though bicyclists
overtaking on the right may get "doored" from the left, or collide with
jaywalking pedestrians and crossing vehicles hidden by the stopped traffic. These risks
require that a cyclist travel very slowly and sometimes avoid moving forward at all, a
limitation that does not occur if the motor traffic is moving faster than the bicycle
traffic or if bicyclists overtake on the left.

If the right lane has zero traffic flow, because it is gridlocked (queue waiting to turn
right, etc.) but the next lane is flowing freely at a nice, comfortable speed for
cyclists, 30 km/h, the level of service rating is D or lower. Clearly the authors never
even addressed bicyclists' using any lane to the left of the rightmost travel lane.

And if there is no motor traffic at all, the quantity in the formula for motor traffic
speed is undefined and the formula fails.

The table below shows results which the formula gives under several conditions with
data in range and out of range. Only the data fields which change are shown. The
calculations including all data fields are included in a Microsoft Excel workbook[5] made available in connection with this
article.

In the upper rows of the table, gridlocked traffic rates a higher LOS than moving
traffic, whether or not there is room on either side of the gridlocked travel lane for
bicyclists to overtake freely.

The bottom few rows illustrate the failure to account for overtaking on the left of
stopped traffic. Note that a bike lane increases the rated level of service, despite the
issues raised earlier about overtaking on the right.

Table comparing levels of service calculated
according to the Bicycle Compatibility Index
(some with parameters out of range)

Reformatted workbook allows comparisons

The Excel workbook provided as part of the BCI package[6] allows entry of data for only one location. This is a
very inefficient and cumbersome use of computer spreadsheet software. I have reformatted
the workbook to allow comparison of data for many locations. My revision does not change
the formulas, and so it does not solve the problems with the BCI, but rather, helps to
reveal them.

I have referenced cells in later workbook sheets to the equivalent cell in the first
sheet -- so it is not necessary to type in the name of the location on all three sheets. I
also have made cells fit more compactly around the text. Each worksheet will now fit
nicely on a 1024 x 768 pixel computer screen at 100% display size. I have also placed the
formulas on the new rows inside conditional statements, so error messages will not display
unless a location is named.

I have highlighted obligatory data entry cells in yellow, cells in which data may be
entered either as a number or as a formula in green, and results in blue. There is one
formatting problem I have not corrected: there are four data entry variables in the second
worksheet, though the names of the worksheets indicate that only the first sheet is
for data entry.

Programming and descriptive errors

In the authors' workbook, one of the data entry cells in the second sheet, for curb
lane truck volume, is supposed to default to a different value depending on the number of
lanes in the street, but the workbook does not automatically set the default value.

Several header cells describe data entry in percentages where the data must be input as
decimal fractions.

There is a serious programming error in the third sheet. The cell for speed (in red)
refers to a header cell in the previous row. I have corrected this problem in the rows I
have added.

The formula, as I have corrected it, carries an assumption that the 85th percentile
speed of traffic is 15 km/hr faster than the speed limit, if an actual 85th percentile
speed is not given. Though the report indicates that the 15 km/h adjustment can be
altered, it must be altered in a formula rather than in a table cell. If an 85th
percentile speed of zero (out of range but common in urban areas) is entered, the
formula will "correct" this to 15 km/h.

As already noted, the workbook does not post error messages if numbers are posted for
conditions outside the range which the BCI is supposed to account for. As many common
traffic conditions are outside its range, I have not attempted to correct this problem in
my revised workbook, because I want users to be able to test the BCI with out-of-range
data.

There are data cells with range limitations imposed by hard mathematical limits -- for
example, parking occupancy can not be higher than 1.00 or lower than 0.00. These cells,
too, would benefit from error trapping, to prevent input of invalid data.

I have highlighted the cells with outright programming and descriptive errors in red,
and I have highlighted cells with range limitations that are within the range of normal
traffic data in purple.

Conclusions and recommendations

While a level of service rating is a useful tool, the Bicycle Compatibility Index is
not a level of service rating, and it is flawed as a comfort rating. It is remarkable that
the FHWA has sanctioned this work in the light of other highly advanced research into
traffic flow that it has generated.[7]

How could a better bicyclist level-of-service rating be developed? That question is
difficult to answer. Let us consider the three primary elements of a rating: mobility,
safety and comfort.

An objective formula for mobility could be developed. though it would be considerably
more complicated than for motor traffic. To give an example, the degree of mobility under
congested conditions depends on lane width and on the composition of the motor traffic.
Even in a completely stalled traffic jam, a bicyclist usually can move forward slowly. And
as described above, traffic signal timing, directness of routing and terrain also strongly
affect bicyclists' mobility, and in ways they do not affect mobility of motorists. On the
other hand, speed limits rarely affect bicyclists, who rarely travel as fast as the posted
speed limit.

Safety of streets also can be at least roughly evaluated based on the results of the
research record. Safety, however, depends very heavily on the level of skill of the
bicyclist, and so no single safety rating is possible. Roadway conditions that are
reasonably safe for an adult bicycle commuter, tourist or fitness rider -- particularly,
one with vehicular cycling skills -- are far less safe for children and casual adult
bicyclists. Conversely, conditions which are reasonably safe for casual cyclists and
children may not be so for faster, experienced adult cyclists. This is particularly so on
multi-use paths, where the presence of pedestrians makes it unsafe to travel at speeds
that fit adult bicyclists easily can attain.

Comfort is the most troublesome variable. Comfort depends primarily on the perceived
level of safety, however, perceptions correlate poorly with actual levels of safety.
Perceptions often are at odds with reality, as evidenced by many examples of bicyclist
behavior such as ducking between parked cars, riding opposite the flow of traffic, and
riding at high speeds on trails that are less suitable than roads for such speeds.

Workable ratings of bicycle routes have been produced by experienced bicyclists. Though
objective factors such as traffic counts, motor vehicle speeds, lane widths and steepness
of climbs play an important part in such ratings, there are other important factors which,
though objective, do not show up in the usual highway department databases -- for example,
quality of pavement near the edge of the road, or the availability of roadside amenities.
A good route surveyor will be familiar with the type of bicyclist who is to use a route --
indeed, must have experience with the type of cycling that is to be accommodated. The
surveyor also must travel the route to experience it firsthand. In the end, a rating may
be based to a large degree on factors that were not even considered before surveying the
route, and which would require an impractical, complicated data structure to quantify. The
rating therefore becomes to some degree subjective. Despite these problems, the success of
ratings developed by and for bicyclists is shown, for example, by the low crash rate on
the Bikecentennial TransAmerica route.[8]
Such ratings are, in the author's opinion, the best ones available.